A centrifuge has: a rotor for holding a test sample stored in a tube or others; and a rotary chamber (a rotor chamber) in which the rotor is placed. When the rotor is rotated at high speed by a driving device configured of an electric-powered motor or others, the test sample held by the rotor is centrifuged. A pressure in the rotary chamber (the rotor chamber) is reduced in order to prevent temperature increase of the rotor caused by windage loss.
Generally, as disclosed in Patent Document 3 (Japanese Patent Application Laid-Open Publication No. 2008-23477), in order to prevent temperature increase of the rotor and the test sample caused by frictional heat (windage loss) between air in the rotary chamber and the rotor, a so-called ultra centrifuge having a rotor with the number of revolutions of exceeding 40,000 includes: a vacuum pump machine for reducing the pressure inside the rotary chamber to a high vacuum state; and a vacuum pressure detecting unit formed of a sensor for detecting a vacuum pressure inside the rotary chamber and a sensor detection circuit.
The vacuum pump machine for reducing the pressure from atmospheric pressure to the high vacuum state includes: an auxiliary vacuum pump for reducing the pressure from the atmospheric pressure to a medium vacuum state whose pressure is about 13 pascals; and an oil diffusion pump for reducing the pressure from the medium vacuum state to the high vacuum state whose pressure is about 1 pascal. The auxiliary vacuum pump and the oil diffusion pump are connected to each other in series. The oil diffusion pump is configured of: a boiler; a heater; a jet stream generating unit; a cooling unit; an inlet; an outlet; and others. The heater heats the boiler, and the boiler heats oil stored therein. Oil molecules heated by the boiler so as to be evaporated and vaporized go up through a center part of the jet stream generating unit, and is powerfully injected downward from a peripheral part thereof. The oil molecules injected at high speed from the jet stream generating unit hit a wall surface of the cooling unit, and are cooled to be liquefied. At this time, gas molecules in periphery of the oil molecules are blown away by the oil molecules to be compressed downward. The inlet is connected to the rotary chamber, and the outlet is connected to the auxiliary vacuum pump.
In order to suppress the temperature increase of the rotor and the test sample caused by the frictional heat between the rotating rotor and the air inside the rotary chamber, a so-called vacuum standby operation in which the rotor is rotated at a predetermined certain small number of revolutions (for example, 5,000 revolutions per minute) is normally performed until the pressure inside the rotary chamber is reduced by the vacuum pump machine to a predetermined pressure (for example, the medium vacuum state whose pressure is about 13 pascals). After the pressure inside the rotary chamber becomes the medium vacuum state, a rotation rate of the rotor is accelerated to several tens of thousands or well over a hundred thousand revolutions per minute.
Alternatively, when it is desired to suppress the temperature increase of the test sample caused by the windage loss of the rotor as much as possible, a so-called vacuum start operation in which the rotor is rotated after the pressure inside the rotary chamber becomes the medium vacuum state is performed.
As disclosed in Patent Document 1 (Japanese Patent Application Laid-Open Publication No. 2001-104826) and Patent Document 2 (Japanese Patent Application Laid-Open Publication No. 2011-25176), in such a centrifuge including the vacuum pump machine, a temperature of the heater which evaporates and vaporizes diffusion oil inside the boiler of the oil diffusion pump is adjusted by the temperature sensor, so that the operation of the oil diffusion pump is controlled.
Also, as disclosed in the Patent Document 3, the operation of the oil diffusion pump is controlled based on a degree of vacuum of the rotary chamber detected by a vacuum sensor.
Further, in the oil diffusion pump used here, an amount of oil for generating the oil jet injection for the vacuuming is not normally controlled. Generally, oil is added or replaced after a necessary degree of vacuum cannot be obtained.